The present invention relates to an ultrasound imaging method and apparatus, and more particularly, to an ultrasound imaging method and apparatus for forming color images by using a power threshold level that is varied depending on a pixel""s position within a color image for isolating noises and color signals.
An ultrasound imaging system with a color mode imaging capability is known to be able to provide a color image in addition to a B (Brightness) mode image. Referring to FIG. 1, an exemplary display of a color image within a color box is shown, wherein reference numerals 1, 2 and 3 indicate a B mode image, a color box, and a color image, respectively.
Conventionally, a power threshold level for isolating noises and color signals is determined as a constant regardless of pixel""s position. Referring to FIG. 2, there is illustrated a graphical representation of a conventional power threshold level 301 and a noise power level 302 corresponding to the pixel""s position along the direction perpendicular to a probe in an image showing a target object. In FIG. 2, the horizontal transverse axis represents depth in an axial direction and the vertical longitudinal axis represents power level. As shown in FIG. 2, the power threshold level 301 has a constant value. Therefore, in the prior art, a color display is determined by comparing the noise power level 302 with the power threshold level 301 regardless of the variation of the noise power level 302 along the depth. Specifically, if the level of an input power is higher than the power threshold level 301, a color corresponding to the input power is displayed. Otherwise, the input power is regarded as a noise, and the corresponding color is not displayed. Use of the power threshold level 301 as noted above causes problems such as weak input powers being regarded as noise. Consequently, a color corresponding to the weak input power may not be displayed on an image.
Further, due to various characteristics depending on the pixel""s position, such as TGC (Time Gain Compensation), an apodization using a function can be varied depending on an axial direction, and the change of aperture size, the gain of a color signal may also be varied depending on the pixel""s position. Specifically, the TGC compensates the ultrasound attenuation caused by the human body such that it makes a pixel in proximity to a transducer have small gain and a pixel out of proximity thereto have large gain. In general, the function varied depending on the axial direction of a scan line is used as an apodization profile and utilized in the apodization that applies different gains to each channel. The aperture size of a scan line in proximity to both edges of a transducer is relatively smaller than that of another scan line. Thus, the actual range of a noise may be varied depending on the above-mentioned characteristics.
Therefore, if a power threshold level having a constant value is used to process a receiving signal, e.g. a color Doppler signal, noise is filtered improperly or a color signal is extremely removed from the receiving signal, thereby deteriorating the quality of images.
It is, therefore, an object of the present invention to provide an ultrasound imaging method and apparatus for forming high-quality color ultrasound images by using a variable power threshold level that is varied depending on the pixel""s position.
It is another object of the present invention to provide an ultrasound imaging method and apparatus capable of obtaining a noise profile depending on the pixel""s position.
According to one aspect of the present invention, there is provided an ultrasound imaging method, comprising the steps of (a) determining a variable power threshold level based on a noise, (b) transmitting ultrasound signals from at least one transducer array to a target object, (c) receiving a first signal including a signal reflected from the target object mixed with a noise, and (d) imaging an ultrasound image of the target object corresponding to the first signal when the power level of the first signal is greater than the variable power threshold level.
According to another aspect of the present invention, there is provided an ultrasound imaging apparatus, comprising, one or more transducer(s) for transmitting an ultrasound signal to an object and receiving a first signal including a reflected signal from the object mixed with a noise, and a digital signal processor for forming an ultrasound image of the object corresponding to the first signal when a power level of the first signal is greater than a variable power threshold level.